The invention relates to a method and an arrangement for the making of Fresnel lenses.
Fresnel lenses have long been used in searchlights, vehicle headlights, and the like, because they have the advantage that although they are light in weight they can be formed with the large diameters and short focal lengths usually associated with more massive lenses. Such Fresnel lenses are formed by molding plastic or glass. The molds for these lenses must be produced by mechanical means, and as a result lower limits are placed on the shortening of the focal length that can actually be achieved if lenses of worthwhile quality are to be produced.
Also known in the art are so-called Fresnel zone plates, which are formed by graphing interfering spherical wavefronts. These Fresnel zone plates have two focal points, that is, these zone plates create both a real and also a virtual image. In addition, the efficiency of such zone plates is somewhat poor, inasmuch as only part of the light incident upon the zones is diffracted.